Method and apparatus for sensing seat occupant weight

ABSTRACT

A system for measuring the weight of a seat occupant is used to control airbag deployment. The system is incorporated into a vehicle seat supported on inboard and outboard track assemblies. The inboard and outboard track assemblies are mounted to a vehicle structure such that a center track portion remains unsupported. A first sensor assembly is mounted to the inboard track assembly and a second sensor assembly is mounted to the outboard track assembly. The first sensor assembly generates a first signal in response to measuring deflection of the inboard track assembly due to seat occupant weight. The second sensor assembly generates a second signal in response to measuring deflection of the outboard track assembly due to seat occupant weight. A central processor determines seat occupant weight based on the first and second signals. The central processor communicates with the airbag system to control the deployment of the airbag based on seat occupant weight.

RELATED APPLICATION

This application is a continuation of U.S. Ser. No. 09/507,868 filedFeb. 22, 2000, which claims priority to U.S. Provisional Application No.60/120,637 filed on Feb. 24, 1999.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method and apparatus for measuring theweight of a seat occupant. Specifically, a sensor arrangement is mountedwithin a vehicle seat track to provide accurate seat occupant weightmeasurements.

2. Related Art

Most vehicles include airbags and seatbelt restraint systems that worktogether to protect the driver and passengers from experiencing seriousinjuries due to a high speed collision. It is important to control thedeployment force of the airbags and the force of the seatbeltpretensioners based on the size of the driver or the passenger. One wayto control these forces is to monitor the weight of the seat occupant.If a smaller person such as a child or infant in a car seat is in thepassenger seat, the weight on the seat will be less than if an adultoccupies the seat.

Current systems for measuring the weight of a seat occupant are complexand expensive. One type of system uses pressure sensitive foil matsmounted within the seat bottom foam. Another system uses sensors placedat a plurality of locations within the seat bottom. The combined outputfrom the mats or the sensors is used to determine the weight of the seatoccupant. These sensors experience a substantially vertical force, dueto the weight of the seat occupant, but are also subject to longitudinaland lateral forces caused by acceleration, deceleration, or turning. Thelateral and longitudinal forces picked up by the sensor incorporate anerror component into the weight measurement. The sensors are verysophisticated using multiple strain gages and complicated bendingelements to provide high measurement sensitivity in the verticaldirection and low sensitivity to lateral and longitudinal forces inorder to increase accuracy.

Mounting these sensors within the seat bottom can also be difficult andtime consuming. It is difficult to find mounting locations for each thesensors that will accommodate all of the various positions of a seatedoccupant while still providing accurate measurements. Further, shiftingof the occupant on the seat can dislodge or move the sensors out oftheir proper location. Because the sensors are mounted within the seatbottom, it is difficult to reposition the sensors after the seat isinstalled in the vehicle.

Thus, it is desirable to have a simplified seat occupant weightmeasurement system that is accurate and easily to install and overcomesthe above references deficiencies with prior art systems.

SUMMARY OF THE INVENTION

In a disclosed embodiment of this invention, a system for measuring theweight of an occupant seated on a vehicle seat includes a track assemblythat is used to support a vehicle seat. The track assembly includes afirst track mounted to a vehicle structure and a second track supportedfor movement relative to the first track. The tracks are deflectable ina vertical direction due to an occupant weight force exerted on theseat. At least one sensor is mounted on the tracks for generating asignal representative of the occupant weight force.

In a preferred embodiment, the track assembly is comprised of an inboardtrack assembly and an outboard track assembly spaced apart from theinboard track assembly. A first sensor assembly is mounted to theinboard track assembly for generating a first signal in response tomeasuring deflection of the inboard track assembly due to seat occupantweight. A second sensor assembly is mounted to the outboard trackassembly for generating a second signal in response to measuringdeflection of the outboard track assembly due to seat occupant weight.The system uses a central processor to determine seat occupant weightbased on the first and second signals. The system also preferablyincludes an airbag control module that is in communication with theprocessor. Deployment force of an airbag is controlled by the controlmodule based on seat occupant weight.

A method for determining the weight of a seat occupant includes thefollowing steps. An inboard seat track assembly is mounted to a vehiclestructure and an outboard seat track assembly is spaced apart from theinboard seat track assembly and mounted to the vehicle structure. Theinboard and outboard seat track assemblies are defined by apredetermined cross-sectional area and each track assembly has at leastone track segment with a cross-sectional area that is less than thepredetermined cross-sectional area. The method steps includes mounting afirst sensor assembly in the track segment of the inboard seat trackassembly, mounting a second sensor assembly in the track segment of theoutboard seat track assembly, generating a first signal from the firstsensor assembly in response to deflection of the inboard track assemblydue to seat occupant weight, generating a second signal from the secondsensor assembly in response to deflection of the outboard track assemblydue to seat occupant weight, and combining the first and second signalsto determine seat occupant weight.

Additional steps include providing a system controller for controllingdeployment of an airbag and generating a seat occupant weight signalbased on the combination of the first and second signal. The seatoccupant weight signal is transmitted to the controller and thedeployment force of the airbag is controlled based on the seat occupantweight.

These and other features of the present invention can be best understoodfrom the following specification and drawings, the following of which isa brief description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a vehicle with an airbag system andan occupant sitting in a seat with the airbag in an active state shownin dashed lines.

FIG. 2 is a side view of a seat assembly incorporating the subjectweight measurement system.

FIG. 3 is a side view of the seat track assembly of FIG. 2.

FIG. 3A is a magnified view of the section 3A indicated in FIG. 3.

FIG. 4 is a cross sectional view of the track assembly taken along lines4-4 of FIG. 3.

FIG. 5 is a schematic view of a control system for the subject weightmeasurement system.

FIG. 6 is a schematic view of the sensors mounted within the subjecttrack assembly.

FIG. 7 is a schematic view representing a full bending bridge.

FIG. 8 is a schematic view of the sensors mounted within the subjecttrack assembly having an overload mechanism.

DETAILED DESCRIPTION OF AN EXEMPLARY EMBODIMENT

A vehicle includes a vehicle seat assembly, shown generally at 12 inFIG. 1, and an airbag system 14. The seat assembly 12 can be either adriver or passenger seat and includes a seat back 16 and a seat bottom18. When a vehicle occupant 20 is seated on the seat 12 a vertical forceFv is exerted against the seat bottom 18. The vertical force Fvrepresents the weight of the seat occupant 20.

The airbag system 14 deploys an airbag 24 under certain collisionconditions. The deployment force for the airbag 24, shown in dashedlines in FIG. 1, varies according to the weight of the occupant 20. Thevehicle includes a unique system for measuring the weight of the seatoccupant 20. This unique system is installed within a seat trackassembly, generally indicated at 26 in FIG. 2.

The seat track assembly 26 includes a first track member 28 mounted to avehicle structure 30 such as a floor, frame, or riser, for example. Asecond track member 32 is supported for movement relative to the firsttrack member 28 along a longitudinal axis 34. First 38 and secondsensors 40 are mounted on one of the track members 28, 32. The sensors38 and 40 are used to generate a signal representative of the occupantweight. The first sensor 38 is preferably positioned rearwardly and thesecond sensor 40 positioned forwardly on the track assembly 26. Thefirst 38 and second 40 sensors are used to measure deflection of thetrack assembly 26 to generate the signal.

The first track member 28 includes a forward end 42 and a rearward end44 with a central track portion 46 extending between the ends 42, 44.The forward 42 and rearward 44 ends are mounted to the vehicle structure30 such that the central track portion 46 remains unsupported to formgap 48 between the vehicle structure 30 and the central track portion46. Preferably, the first track member 28 is mounted to a riser 50having upwardly extending supports 52 at each end for attachment to theforward 42 and rearward 44 ends of the first track member 28.

Thus, the central track portion 46 of the seat track assembly 26 isdeflectable under load. When the occupant is seated on the seat 12, avertical force Fv is exerted against the track assembly 26, as shown inFIG. 3. Reaction forces Fr are exerted in the opposite direction. Theforces cause the central track portion 46 to deflect and reflect fullbending beam behavior, shown generally at 54 in FIG. 3A. The sensors arepreferably strain gages 38, 40 that are positioned along the centraltrack portion 46, however, other types of sensors known in the art couldalso be used. For example, fiber optic or magneto elastic sensors couldbe used.

The sensors 38, 40 are preferably positioned in the first track member28 such that the sensors 38, 40 remain positioned in the unsupportedtrack section as the second track member 32 adjusts horizontally alongaxis 34. As shown in FIG. 4, a plurality of ball bearings 56 areinstalled between the track members 28, 32 such that the second trackmember 32 can slide easily relative to the first track member 28. Thebearings 56 also transfer the forces applied to the second track member32 to the rigid central track portion 46 between the two (2) sensorlocations.

As shown in FIG. 5, the seat 12 is mounted to the vehicle structure 30on an inboard track assembly 26 a and an outboard track assembly 26 bthat is spaced apart from the inboard track assembly 26 a by apredetermined distance. The inboard 26 a and outboard 26 b trackassemblies are mounted to have similar bending behavior, i.e. both trackassemblies 26 a, 26 b are deflectable in a vertical direction due to anoccupant weight force. Both the inboard 26 a and outboard 26 b trackassemblies include first 28 and second 32 track members.

In one embodiment, first 38 and second 40 sensors are installed in theinboard track assembly 26 a and third 58 and fourth 60 sensors areinstalled in the outboard track assembly 26 b. The first 38 and second40 sensors generate a first signal 62 representative of the portion ofoccupant weight on the inboard track assembly 26 a and the third 58 andfourth 60 sensors generate a second signal 64 representative of theportion of occupant weight on the outboard track assembly 26 b. Thesignals 62, 64 are transmitted to an electronic control unit (ECU) 66,which combines the signals to determine the weight of the occupant 20.The ECU then sends a control signal 68 to a system controller 70.Preferably, the system controller 70 is an airbag control module that isin communication with the ECU 66 such that the deployment force of theairbag 24 is controlled based on seat occupant weight. The systemcontroller 70 could also be used to control the force of seat beltpretensioners based on occupant weight.

While the above configuration is preferred, an option configurationcould utilize one sensor assembly mounted to the inboard track assemblyfor generating the first signal 62 in response to measuring deflectionof the inboard track assembly 26 a due to seat occupant weight and asecond sensor assembly mounted to the outboard track assembly 26 b forgenerating the second 64 signal in response to measuring deflection ofthe outboard track assembly 26 b due to seat occupant weight.

As shown in greater detail in FIG. 6, the track assembly 26 has apredetermined cross-sectional area defined by height H1. A trackportion, generally indicated at 72, of each track assembly 26 has across-sectional area defined by H2 that is less than the predeterminedcross-sectional area H1. Each track assembly 26 a, 26 b has two (2)track portions 72 with this decreased cross-sectional area. One sensorassembly 38, 40, 58, 60 is mounted in each track portion 72. Only thefirst sensor assembly 38 is shown in FIG. 6. As the track assembly 26deflects under load, the sensor assembly 38 measures full bending beambehavior 54, shown in FIG. 7. Each of the sensors 38, 40, 58, 60 at thefour (4) locations thus serves as a Wheatstone Bridge for measuringdeflection. The operation of a Wheatstone Bridge is well known in theart.

Preferably, the reduced cross-sectional area track portions 72 arecreated by forming square shaped holes within the first track member 28.The holes create dual-beam spring elements. With such elements locatedon the inboard 26 a and outboard 26 b track assemblies, it is possibleto measure the vertical force Fv applied on the area between the twosets of tracks 26 a, 26 b.

The method for determining the weight of a seat occupant includes thefollowing steps. An inboard seat track assembly 26 a is mounted to avehicle structure 30 and an outboard seat track assembly 26 b is spacedapart from the inboard seat track assembly 26 a and mounted to thevehicle structure 30. The inboard 26 a and outboard 26 b seat trackassemblies are defined by a predetermined cross-sectional area H1 andeach track assembly 26 a, 26 b has at least one track portion 72 with across-sectional area H2 that is less than the predeterminedcross-sectional area H1. The method steps include mounting a firstsensor assembly in the track portion 72 of the inboard seat trackassembly 26 a and mounting a second sensor assembly in the track portion72 of the outboard seat track assembly 26 b. A first signal 62 isgenerated from the first sensor assembly in response to deflection ofthe inboard track assembly 26 a due to seat occupant weight. A secondsignal 64 is generated from the second sensor assembly in response todeflection of the outboard track assembly 26 b due to seat occupantweight. The first 62 and second 64 signals are used to determine seatoccupant weight.

Additional steps include providing a system controller 70 forcontrolling deployment of an airbag 24 and generating a seat occupantweight signal based on the combination of the first 62 and second 64signals. The seat occupant weight signal is transmitted to thecontroller and the deployment force of the airbag is controlled based onthe seat occupant weight.

Other steps include providing the inboard 26 a and outboard 26 b trackassemblies with forward ends 42 and rearward 44 ends interconnected bythe central track portion 46 and fixing the forward 42 and rearward 44ends to the vehicle structure 30 such that the central track portion 46of each track assembly 26 a, 26 b remains unsupported. The track portion72 is preferably located in the central track portion 46.

As discussed above, the first sensor assembly is preferably comprised offirst 38 and second 40 sensors that are mounted in the first trackmember 28 of the inboard track assembly 26 a. The second sensor assemblyis preferably comprised of third 58 and fourth 60 sensors that aremounted in the first track member 28 of the outboard track assembly 26b.

A seat track assembly 26 with integrated weight sensors 38, 40, 58, 60is provided to determine the weight of an occupant 20 seated on avehicle seat 12. It is preferable to integrate the sensors 38, 40, 58,60 into the seat track assembly 26 because it is a common component formost vehicle seats 12. The subject weight measurement system is easilyincorporated into any type of seat track configuration. The weightsensors 38, 40, 58, 60 are mounted within reduced size track portions 72to measure deflection of the track material caused by the weight of theoccupant 20. The measured weight is independent of seat positions and isaccurately provided in various occupant positions on the seat 12.

By measuring the deflection in all four (4) locations in the inboard 26a and outboard 26 b track assemblies, it is possible to calculate theoccupant weight, which is proportional to the sum of the output of allof the sensors 38, 40, 58, 60. The center of gravity of the upper partof the seat and the occupant can be calculated by subtracting the sum ofthe sensor signals in the front from the sum of the sensor signals inthe rear and dividing the result by the sum of all four (4) signals. Theelectronics for signal conditioning can be housed within the trackassemblies 26 a, 26 b as is well known in the art.

Under high overload conditions, the track assembly 26 experiences highvertical Fv and horizontal Fh forces. These forces cause the track toexperience an overload resultant force Fre that will try to separate thetrack 26 from the floor 30. In applications, with heavy overloadconditions, like seats having integrated or all-belts-to seatconfigurations, it is beneficial to integrate an active overloadprotection. One such method of protection utilizes an overload bolt 74,shown in FIG. 8, extending through the track members 28, 32 to thevehicle floor 30. Under high vehicle impact forces, the bolt 74 preventsthe track assembly 26 from separating from the floor 30. Thus, thereduced cross-sectional areas of track portion 72 do not have to sustainthe full impact forces.

Although a preferred embodiment of this invention has been disclosed, itshould be understood that a worker of ordinary skill in the art wouldrecognize many modifications come within the scope of this invention.For that reason, the following claims should be studied to determine thetrue scope and content of this invention.

1. A system for measuring weight of an occupant seated on a vehicle seatcomprising: a first track mountable to a vehicle structure; a secondtrack supported for movement relative to said first track for adjustmentalong a longitudinal axis and being deflectable in a vertical directiondue to an occupant weight force generated by the occupant sitting on thevehicle seat; at least one sensor mounted to said first track forgenerating a signal representative of said occupant weight force; and acentral processor for receiving said signal.
 2. A system according toclaim 1 including an airbag control module in communication with saidcentral processor wherein deployment force of an airbag is controlled bysaid airbag control module based on seat occupant weight.
 3. A systemaccording to claim 2 wherein said first track includes a forward end anda rearward end with a central track portion extending between saidforward and rearward ends, said forward and rearward ends being mountedto the vehicle structure such that said central track portion remainsunsupported to form a gap between the vehicle structure and the centraltrack portion.
 4. A system according to claim 3 wherein said at leastone sensor is positioned along said central track portion.
 5. A systemaccording to claim 4 wherein said at least one sensor is comprised of afirst sensor positioned forwardly on said central track portion and asecond sensor positioned rearwardly on said central track portion, saidfirst and second sensors for measuring deflection of said second trackto generate said signal.
 6. A system according to claim 5 including athird track mounted to the vehicle structure, a fourth track supportedfor movement relative to said third track for adjustment along alongitudinal axis and being deflectable in a vertical direction due tosaid occupant weight force generated by the occupant sitting on thevehicle seat, and a third sensor mounted on one of said third or fourthtracks working with said first and second sensors to generate saidsignal, said first and second tracks forming an inboard track assemblyand said third and fourth tracks forming an outboard track assembly. 7.A system for measuring seat occupant weight comprising: a first seattrack adapted to be fixed to a vehicle structure; a second seat tracksupported for movement relative to said first seat track for adjustmentalong a longitudinal axis, said first and second seat tracks beingdeflectable in a direction transverse to said longitudinal axis due toan occupant weight force generated by an occupant sitting on a vehicleseat; and at least one sensor mounted directly to said first seat trackto generate a weight signal by measuring deflection of said first andsecond seat tracks due to seat occupant weight.
 8. A system according toclaim 7 wherein said first seat track includes a forward end and arearward end with a central portion extending between said forward andrearward ends, said forward and rearward ends being mountable to thevehicle structure such that said central portion remains unsupported toform a gap between the vehicle structure and said central portion.
 9. Asystem according to claim 7 wherein said first track and said secondtrack form an inboard track assembly and wherein said at least onesensor comprises a first sensor assembly mounted to said inboard trackassembly for generating a first signal in response to measuringdeflection of said inboard track assembly and a second sensor assemblymounted to an outboard track assembly spaced apart from said inboardtrack assembly, said second sensor assembly for generating a secondsignal in response to measuring deflection of said outboard trackassembly and including a central processor for determining seat occupantweight based on said first and second signals.
 10. A system according toclaim 9 wherein said outboard track assembly comprises a third trackmountable to the vehicle structure and a fourth track mounted formovement relative to said second track and wherein said first sensorassembly is mounted to said first track and said second sensor assemblyis mounted to said third track.
 11. A system for measuring weight of anoccupant seated on a vehicle seat comprising: a first track mountable toa vehicle structure; a second track supported for movement relative tosaid first track for adjustment along a longitudinal axis and beingdeflectable in a direction transverse to said longitudinal axis due toan occupant weight force exerted on the vehicle seat; at least onesensor mounted on one of said first and second tracks for generating asignal representative of said occupant weight force wherein said firsttrack and said second track form an inboard track assembly and whereinsaid at least one sensor comprises a first sensor assembly mounted tosaid inboard track assembly for generating a first signal in response tomeasuring deflection of said inboard track assembly and a second sensorassembly mounted to an outboard track assembly spaced apart from saidinboard track assembly, said second sensor assembly for generating asecond signal in response to measuring deflection of said outboard trackassembly wherein said inboard and outboard track assemblies have apredetermined cross-sectional area with each track assembly having atleast one track portion having a cross-sectional area that is less thansaid predetermined cross-sectional area, said first and second sensorassemblies being mounted on said track portion; and a central processorfor determining seat occupant weight based on said first and secondsignals.
 12. A system according to claim 11 wherein said inboard andoutboard track assemblies each include a forward end and a rearward endwith a central portion extending between said forward and rearward ends,said forward and rearward ends being mounted to the vehicle structuresuch that said central portions are unsupported forming a gap betweenthe vehicle structure and the inboard and outboard track assemblies. 13.A system according to claim 12 wherein said at least one track portion,with said cross-sectional area that is less than said predeterminedcross-sectional area, is located in said central portion.
 14. A systemaccording to claim 12 wherein said at least one track portion of each ofsaid inboard and outboard track assemblies is comprised of a first trackportion located forwardly in said central portion and a second trackportion located rearwardly in said central portion and wherein saidfirst and second sensor assemblies each include a first sensor mountedon said first track portion and a second sensor mounted on said secondtrack portion.
 15. A system according to claim 12 including an airbagcontrol module in communication with said central processor whereindeployment force of an airbag is controlled by said airbag controlmodule based on seat occupant weight.
 16. A method for determiningweight of a seat occupant comprising the steps of: providing a firsttrack adapted for mounting to a vehicle structure and a second tracksupported for movement relative to the first track along an axis to forma first track assembly; providing a second track assembly spaced apartfrom the first track assembly with the second track assembly including athird track adapted for mounting to the vehicle structure and a fourthtrack supported for movement relative to the third track along an axisand wherein the first and second track assemblies are defined by apredetermined cross-sectional area and each track assembly has at leastone track segment with a cross-sectional area that is less than thepredetermined cross-sectional area; mounting a first sensor assembly tothe first track assembly by mounting the first sensor assembly to thefirst track in the track segment of the first track assembly; mounting asecond sensor assembly to the second track assembly by mounting thesecond sensor assembly to the third track in the track segment of thesecond track assembly; generating a first signal from the first sensorassembly in response to deflection of the first track assembly in adirection transverse to the axis due to seat occupant weight generatedby the occupant sitting on the vehicle seat; generating a second signalfrom the second sensor assembly in response to deflection of the secondtrack assembly in a direction transverse to the axis due to seatoccupant weight generated by the occupant sitting on the vehicle seat;and combining the first and second signals to determine seat occupantweight.
 17. A method according to claim 16 including the step ofproviding a system controller for controlling deployment of an airbag;generating a seat occupant weight signal based on the combination of thefirst and second signals; transmitting the seat occupant weight signalto the controller; and controlling a deployment force of the airbagbased on the seat occupant weight.
 18. A method according to claim 16including the steps of providing the first and second track assemblieswith forward ends and rearward ends interconnected by a center portionand fixing the forward and rearward ends to the vehicle structure suchthat the center portion of each track assembly remains unsupported. 19.A method according to claim 18 including the step of locating the tracksegment in the center portion.
 20. A method according to claim 16wherein the first sensor assembly is comprised of a first sensor mountedrearwardly within the first track assembly and a second sensor mountedforwardly within the first track assembly and wherein the second sensorassembly is comprised of a third sensor mounted rearwardly within thesecond track assembly and a fourth sensor mounted forwardly within thesecond track assembly.